I own a 24x60' uninsulated building that's about 100 years old. The roof is matched 2x4 rafters (no ridge board) with 2x4 ceiling joist (technically rafter ties I guess). As you can imagine, the joists are sagging quite substantially. Previous owners have tried to fix it with a mix of various methods. I want it fixed one and for all because I'm planning on drywalling and insulating the building.
I don’t think I can put in bigger joist because there would be no room to fit them at the top plate. Definitely not the 2x12's that would be required. I'd really rather not put in posts and beam because the ceiling is only 8' high.
My thought is to jack a joist straight, sister a 4’ 2x4 to it in the middle, tie the now straight joist to a strongback. Would this provide enough support to hold the sag out and support drywall and insulation?